EP2816125A1 - Process for producing low-cost clean steel - Google Patents

Process for producing low-cost clean steel Download PDF

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Publication number
EP2816125A1
EP2816125A1 EP12871396.3A EP12871396A EP2816125A1 EP 2816125 A1 EP2816125 A1 EP 2816125A1 EP 12871396 A EP12871396 A EP 12871396A EP 2816125 A1 EP2816125 A1 EP 2816125A1
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EP
European Patent Office
Prior art keywords
ball
desulfurizing
dephosphorizing
cao
during
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP12871396.3A
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German (de)
French (fr)
Other versions
EP2816125A4 (en
EP2816125B1 (en
Inventor
Fuping Tang
Zhen Li
Xiaofeng Wang
Peng Fei
Jinsong Meng
Yue Zhang
Yong Ma
Wenzhong Wang
Zhiwen Zhang
Xiaoshan WANG
Meng Guo
Zhigang Zhao
Yang Lin
Guoqiang XIN
Weizhi YAO
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Angang Steel Co Ltd
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Angang Steel Co Ltd
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Publication of EP2816125A1 publication Critical patent/EP2816125A1/en
Publication of EP2816125A4 publication Critical patent/EP2816125A4/en
Application granted granted Critical
Publication of EP2816125B1 publication Critical patent/EP2816125B1/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/064—Dephosphorising; Desulfurising
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/02—Dephosphorising or desulfurising
    • C21C1/025—Agents used for dephosphorising or desulfurising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C21C5/30—Regulating or controlling the blowing
    • C21C5/35—Blowing from above and through the bath
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C21C5/36—Processes yielding slags of special composition
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0037—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 by injecting powdered material
    • C21C7/0043—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 by injecting powdered material into the falling stream of molten metal
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0087—Treatment of slags covering the steel bath, e.g. for separating slag from the molten metal
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/064—Dephosphorising; Desulfurising
    • C21C7/0645—Agents used for dephosphorising or desulfurising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C2300/00—Process aspects
    • C21C2300/08—Particular sequence of the process steps
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0068—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 by introducing material into a current of streaming metal
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/072—Treatment with gases

Definitions

  • the present invention relates to a steel production technology, and more particularly to a method for preparing low-cost clean steel, which belongs to a field of metallurgical technology
  • Cleanliness is an important sign reflecting overall quality of steel. The cleanliness is usually judged from content of harmful elements in the steel, and number, shape as well as size of non-metallic inclusions. "Clean and pure" steel is typically obtained by reducing and controlling residual elements such as P, S, N, H, T.O, C, Al, and Ti in the steel. The elements affect steel performance in a single or combined form.
  • C, N, and T.O should be less than 20ppm. Diameter of inclusion in tire radial should be less than 10 ⁇ m. In order to improve the anti-contact fatigue performance, T.O in ball bearing steel should be less than 10ppm, or even lower. With the rapid development of steel metallurgy technology for improving the cleanliness, T.O + N + P + S + H in the steel has been equal to or less than 80ppm during production.
  • CN1480549 published March 10, 2004 , discloses a barium-contained clean steel and a production method thereof, which relates to a field of alloy steel, and particularly to barium-contained alloy steel.
  • the production method of the barium-contained clean steel comprises steps of: after melted in a conventional electric furnace, converter, or other vacuum melting furnace, refining in a refining apparatus, and barium-alloying at a late stage of refining; before adding a barium alloying element, adding aluminum deoxidizer or silica-aluminum for pre-deoxidizing, then blowing argon, and adding barium alloy for producing the barium-contained clean steel.
  • the cleanliness of the final product is not sufficient, and the published element percentages by weight in the clean steel are: Ba 0.0001 ⁇ 0.04%, S ⁇ 0.035%, P ⁇ 0.035%, A, B, C and D type inclusions are generally of 1.0-0.5 degree, which do not meet the requirements of a higher cleanliness.
  • clean steel standard is not only a technical problem.
  • the cleanliness object is usually able to be achieved.
  • the production cost is bound to increase, and the user has to pay for the desired high cleanliness.
  • an object of the present invention is to provide a high-quality steel material with S at 5 ⁇ 20ppm, P at 20 ⁇ 60ppm, an overall oxygen content at 3 ⁇ 15ppm, and an inclusion equivalent diameter at 0.5 ⁇ 10 ⁇ m, and to provide a method for preparing low-cost clean steel by which a cost is effectively lowered.
  • the present invention provides a method for preparing low-cost clean steel, comprising steps of:
  • an amount of the desulfurizing ball is 2 ⁇ 8kg/t.
  • an amount of the dephosphorizing ball is 3 ⁇ 12kg/t
  • blowing strength of the argon is 30Nm 3 ⁇ t -1 ⁇ h ⁇ 150 Nm 3 ⁇ t -1 ⁇ h
  • a blowing and stirring time of the argon is 0 ⁇ 7min.
  • a downing tube is at an opposite side of a feeding opening.
  • the desulfurizing ball, the dephosphorizing ball and the purifying ball are all produced by dry-pressing, sizes thereof are 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s.
  • the CaO in the purifying ball comprises MgO and CaO with any mixing ratio.
  • the CaCO 3 in the purifying ball comprises MgCO 3 and CaCO 3 with any mixing ratio, and a particle size of the MgCO 3 is less than 100 ⁇ m.
  • the Ca powder in the purifying ball comprises Mg powder and Ca powder with any mixing ratio, and particle sizes of the Mg powder and the Ca powder are less than 1 mm.
  • MgO activity ⁇ 200ml, and CaO activity ⁇ 200ml Preferably, MgO activity ⁇ 200ml, and CaO activity ⁇ 200ml.
  • the conventional charging methods of iron and steel metallurgy are directly adding block material or blowing powder. If the block material is added, a melting time is long, energy consumption is large, and uneven composition is easy to be caused. If the powder is blown, during charging materials, blowing loss is large, and cost of steelmaking is high.
  • the present invention provides a new charging method, namely reaction-induced micro heterogeneous, which means adding block material into steel melt and then forming powder in the steel melt by burst reaction.
  • balls with the above functions are designed.
  • the ball will decompose at a high temperature, and release micro bubbles as well as slag drops.
  • the micro bubbles will be generated in the steel melt.
  • the micro bubbles are able to uniformize composition and temperature of the steel melt, and the inclusions are directly removed with capture and adsorption effects of the micro bubbles.
  • CaCO 3 , MgCO 3, or (CaCO 3 + MgCO 3 ) composite powder is utilized as a situ agent for generating the micro bubbles.
  • High-temperature decomposition of the CaCO 3 and the MgCO 3 are as follows:
  • a size of a bubble generated is about a size of the powder. Therefore, the method is able to add ultra-fine bubbles into the steel melt (wherein the size of the bubble is between 100 ⁇ 300 ⁇ m). The smaller the bubbles are, the higher inclusion removal efficiency will be.
  • alkaline earth oxides another product of the decomposition reaction of carbonate, will be rapidly melted in the steel melt for forming the slag drops with a slag washing effect. Because of low reaction temperature of decomposition of the carbonates and poor thermal stability thereof, the disadvantage must be eliminated by reasonable designs.
  • the CaO, MgO, (CaO + MgO) composite powder or the white slags cool-collected by the ladle furnace is utilized as a carrier of the carbonate powder.
  • the carrier and the carbonate powder into the ball With a certain size, the thermal stability of the carbonate in the steel melt is improved.
  • Advantages of the present invention are as follows. Process is simple, and operation is convenient. Different balls are respectively added during the blast furnace tapping, the iron folding in the iron folding room, the converter tapping, and the late stage of the RH refining, so as to rapidly desulfurize, dephosphorize, and remove the small inclusions in the steel melt by slag-forming. Furthermore, the P and S contents in the steel are significantly reduced, while quantity and size distribution of small non-metallic inclusions remaining in the steel during refining is effectively controlled. With the method according to the present invention, S in the steel is controlled at 5 ⁇ 20ppm, P is controlled at 20 ⁇ 60ppm, the overall oxygen content is controlled at 3 ⁇ 15ppm, and the inclusion equivalent diameter is controlled at 0.5 ⁇ 10 ⁇ m. Compared with the conventional process, raw materials utilized in the method are cheap, the cost for the steel per ton is reduced by 5-10 Yuan.
  • the present invention provides a method for preparing low-cost clean steel, comprising steps of:
  • the desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 20kg; CaO 50kg; CaF 2 15kg; and CaCO 3 15kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the desulfurizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 65kg; CaO 10kg; CaF 2 1 kg; and CaCO 3 5kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 10kg; CaO 65kg; CaF 2 15kg; CaCO 3 30kg; and Ca powder 15kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, and a particle size of the Ca powder is less than 1 mm.
  • MgO activity ⁇ 200ml MgO activity ⁇ 200ml, and CaO activity ⁇ 200ml.
  • the desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 55kg; CaO 20kg; CaF 2 5kg; and CaCO 3 5kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the desulfurizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 10kg; CaO 65kg; CaF 2 15kg; and CaCO 3 30kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 60kg; MgO 15kg; CaF 2 1kg; MgCO 3 5kg; and Mg powder 1 kg; particle sizes of the CaF 2 , MgCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, and a particle size of the Mg powder is less than 1 mm.
  • Other features of the preferred embodiment 2 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
  • the desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 35kg; CaO 35kg; CaF 2 10kg; and CaCO 3 10kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the desulfurizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 38kg; CaO 38kg; CaF 2 10kg; and CaCO 3 12kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 35kg; mixed powder of CaO and MgO with any mixing ratio 40kg; CaF 2 7kg; mixed powder of CaCO 3 and MgCO 3 with any mixing ratio 15kg; and Ca powder 1 kg; particle sizes of the CaO, CaF 2 , CaCO 3 , MgCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, and a particle size of the Ca powder is less than 1mm.
  • Other features of the preferred embodiment 3 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
  • the desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45kg; CaO 40kg; CaF 2 13kg; and CaCO 3 12kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the desulfurizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 41kg; CaO 45kg; CaF 2 5kg; and CaCO 3 20kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 20kg; mixed powder of CaO and MgO with any mixing ratio 55kg; CaF 2 3kg; CaCO 3 20kg; and Ca powder 12kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, and a particle size of the Ca powder is less than 1mm.
  • Other features of the preferred embodiment 4 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
  • the desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 25kg; CaO 30kg; CaF 2 8kg; and CaCO 3 14kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the desulfurizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 20kg; CaO 55kg; CaF 2 12kg; and CaCO 3 10kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 40kg; MgO 30kg; CaF 2 11 kg; mixed powder of CaCO 3 and MgCO 3 with any mixing ratio 25kg; and mixed powder of Ca powder and Mg powder with any mixing ratio 13kg; particle sizes of the CaF 2 , CaCO 3 , MgCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, and particle sizes of the Ca powder and Mg powder are less than 1 mm.
  • Other features of the preferred embodiment 5 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
  • the desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 30kg; CaO 45kg; CaF 2 6kg; and CaCO 3 9kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the desulfurizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 50kg; CaO 25kg; CaF 2 8kg; and CaCO 3 22kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 50kg; CaO 20kg; CaF 2 4kg; MgCO 3 10kg; and Ca powder 5kg; particle sizes of the CaO, CaF 2 , MgCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, and a particle size of the Ca powder is less than 1mm.
  • Other features of the preferred embodiment 6 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
  • the desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 50kg; CaO 48kg; CaF 2 7kg; and CaCO 3 9kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the desulfurizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45kg; CaO 25kg; CaF 2 3kg; and CaCO 3 8kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45kg; CaO 25kg; CaF 2 5kg; MgCO 3 15kg; and Mg powder 4kg; particle sizes of the CaO, CaF 2 , MgCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, and a particle size of the Mg powder is less than 1mm.
  • Other features of the preferred embodiment 7 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
  • the desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45kg; CaO 25kg; CaF 2 12kg; and CaCO 3 7kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the desulfurizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 28kg; CaO 35kg; CaF 2 13kg; and CaCO 3 18kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5 ⁇ 25mm, compression strength thereof is 5 ⁇ 35MPa, and a reaction time of delay burst at 1600°C is 1 ⁇ 35s;
  • the purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 25kg; mixed powder of CaO and MgO with any mixing ratio 35kg; CaF 2 13kg; CaCO 3 7kg; and mixed powder of Ca powder and Mg powder with any mixing ratio 11 kg; particle sizes of the CaO, CaF 2 , CaCO 3 and the white slags cool-collected by the ladle furnace are less than 100 ⁇ m, and particle sizes of the Ca powder and Mg powder are less than 1 mm.
  • Other features of the preferred embodiment 8 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
  • a conventional method for preparing clean steel comprises steps of:
  • test data of S and P control, total oxygen control, and inclusion control in the steel illustrate that the method according to the present invention is superior to the method in the comparison in both single control and overall control. Furthermore, for the high-quality steel provided by the present invention, S in the steel is controlled at 5 ⁇ 20ppm, P is controlled at 20 ⁇ 60ppm, the overall oxygen content is controlled at 3 ⁇ 15ppm, and the inclusion equivalent diameter is controlled at 0.5 ⁇ 10 ⁇ m.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Analytical Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
  • Carbon Steel Or Casting Steel Manufacturing (AREA)

Abstract

A method for preparing low-cost clean steel includes steps of: preliminarily desulfurizing iron melt: preliminarily desulfurizing in an iron melt channel during blast furnace tapping and during iron folding in an iron folding room, adding a desulfurizing ball into the iron melt during the blast furnace tapping or the iron folding; dephosphorizing and controlling sulfur: dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P ≤ 0.014% and S ≤ 0.004% during tapping; rapidly dephosphorizing by slag-forming: rapidly dephosphorizing by slag-forming during converter tapping, at a converter end point, controlling a C content at 0.02∼0.10%, adding a dephosphorizing ball through an alloy chute during the converter tapping, blowing argon and stirring at the same time; purifying steel melt during RH refining: adding a purifying ball at a late stage of the RH refining when a vacuum degree is at 66.7∼500Pa; and continuously casting with whole-process protection. According to the present invention, steel quality is effectively improved while cost is lowered. Compared with the conventional process, raw materials utilized in the method are cheap, the cost per ton of steel is reduced by5-10 Yuan.

Description

    Field of Invention
  • The present invention relates to a steel production technology, and more particularly to a method for preparing low-cost clean steel, which belongs to a field of metallurgical technology
    • Background Art
  • Cleanliness is an important sign reflecting overall quality of steel. The cleanliness is usually judged from content of harmful elements in the steel, and number, shape as well as size of non-metallic inclusions. "Clean and pure" steel is typically obtained by reducing and controlling residual elements such as P, S, N, H, T.O, C, Al, and Ti in the steel. The elements affect steel performance in a single or combined form. In order to improve the intrinsic quality and performance of the steel, basic requirements for iron and steel metallurgy technology development are: (1) maximizing removal of harmful elements such as S, P, N, H, and T.O (wherein sometimes C is comprised) in steel; (2) precisely controlling element contents in steel; (3) strictly controlling inclusion quantity, composition, morphology, size and distribution, and converting the inclusion to harmless or even beneficial elements; and (4) casting without defect. With development and application of clean steel metallurgy technology, requirements for ferroalloy and auxiliary materials for steelmaking are stricter. For example, in order to meet the increasing toughness requirements for pipeline steel, especially the increasing requirement for HIC-resistance performance of acidic gas pipeline, the content of S in the steel keeps decreasing. For auto sheet (or car shell), C, N, and T.O should be less than 20ppm. Diameter of inclusion in tire radial should be less than 10µm. In order to improve the anti-contact fatigue performance, T.O in ball bearing steel should be less than 10ppm, or even lower. With the rapid development of steel metallurgy technology for improving the cleanliness, T.O + N + P + S + H in the steel has been equal to or less than 80ppm during production. CN1480549, published March 10, 2004 , discloses a barium-contained clean steel and a production method thereof, which relates to a field of alloy steel, and particularly to barium-contained alloy steel. The production method of the barium-contained clean steel comprises steps of: after melted in a conventional electric furnace, converter, or other vacuum melting furnace, refining in a refining apparatus, and barium-alloying at a late stage of refining; before adding a barium alloying element, adding aluminum deoxidizer or silica-aluminum for pre-deoxidizing, then blowing argon, and adding barium alloy for producing the barium-contained clean steel. However, the cleanliness of the final product is not sufficient, and the published element percentages by weight in the clean steel are: Ba 0.0001∼0.04%, S ≤ 0.035%, P ≤ 0.035%, A, B, C and D type inclusions are generally of 1.0-0.5 degree, which do not meet the requirements of a higher cleanliness.
  • In addition, clean steel standard is not only a technical problem. First of all, it is an economic problem. For producers to improve the cleanliness of steel with their own equipments and technology, unless the required cleanliness is too high, the cleanliness object is usually able to be achieved. As a result, the production cost is bound to increase, and the user has to pay for the desired high cleanliness.
    • Summary of the present Invention
  • For overcoming disadvantages of conventional clean steel production, an object of the present invention is to provide a high-quality steel material with S at 5∼20ppm, P at 20∼60ppm, an overall oxygen content at 3∼15ppm, and an inclusion equivalent diameter at 0.5∼10µm, and to provide a method for preparing low-cost clean steel by which a cost is effectively lowered.
  • Accordingly, in order to accomplish the above object, the present invention provides a method for preparing low-cost clean steel, comprising steps of:
    1. 1) preliminarily desulfurizing iron melt: preliminarily desulfurizing in an iron melt channel during blast furnace tapping and during iron folding in an iron folding room, adding a desulfurizing ball into the iron melt during the blast furnace tapping or the iron folding, in such a manner that S ≤ 0.01 % by weight in the iron melt after preliminarily desulfurizing;
    2. 2) pre-desulfurizing the iron melt: finely desulfurizing the iron melt by dusting desulfurization, and filtering out desulfurized slags by a slag filter, in such a manner that after finely desulfurizing, S ≤ 0.0015% by weight in the iron melt before being sent into a converter;
    3. 3) dephosphorizing and controlling sulfur: dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P ≤ 0.014% and S ≤ 0.004% during tapping;
    4. 4) rapidly dephosphorizing by slag-forming: rapidly dephosphorizing by slag-forming during converter tapping; at a converter end point, controlling a C content at 0.02∼0.10%, controlling an oxygen activity value α O at 600∼1000ppm, adding a dephosphorizing ball through an alloy chute during the converter tapping, blowing argon and stirring at the same time;
    5. 5) purifying steel melt during RH refining: adding a purifying ball at a late stage of the RH refining when a vacuum degree is at 66.7∼500Pa; and
    6. 6) continuously casting with whole-process protection;
    wherein the desulfurizing ball comprises: white slags cool-collected by a ladle furnace 20∼55%, CaO 20∼50%, CaF2 5∼15%, and CaCO3 5∼15% by weight, wherein particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm;
    wherein the dephosphorizing ball comprises: white slags cool-collected by a ladle furnace 10∼65%, CaO 10∼65%, CaF2 1∼15%, and CaCO3 5∼30% by weight, particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm; and
    wherein the purifying ball comprises: white slags cool-collected by a ladle furnace 10∼60%, CaO 15∼65%, CaF2 1∼15%, CaCO3 5∼30%, and Ca powder 1∼15% by weight, particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm.
  • Preferably, in the step 1), an amount of the desulfurizing ball is 2∼8kg/t.
  • Preferably, in the step 4), an amount of the dephosphorizing ball is 3∼12kg/t, blowing strength of the argon is 30Nm3·t-1·h∼150 Nm3·t-1·h, and a blowing and stirring time of the argon is 0∼7min.
  • Preferably, in the step 5), when adding the purifying ball, a downing tube is at an opposite side of a feeding opening.
  • Preferably, the desulfurizing ball, the dephosphorizing ball and the purifying ball are all produced by dry-pressing, sizes thereof are 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s.
  • Preferably, the CaO in the purifying ball comprises MgO and CaO with any mixing ratio.
  • Preferably, the CaCO3 in the purifying ball comprises MgCO3 and CaCO3 with any mixing ratio, and a particle size of the MgCO3 is less than 100µm.
  • Preferably, the Ca powder in the purifying ball comprises Mg powder and Ca powder with any mixing ratio, and particle sizes of the Mg powder and the Ca powder are less than 1 mm.
  • Preferably, MgO activity ≥ 200ml, and CaO activity ≥ 200ml.
  • The conventional charging methods of iron and steel metallurgy are directly adding block material or blowing powder. If the block material is added, a melting time is long, energy consumption is large, and uneven composition is easy to be caused. If the powder is blown, during charging materials, blowing loss is large, and cost of steelmaking is high. The present invention provides a new charging method, namely reaction-induced micro heterogeneous, which means adding block material into steel melt and then forming powder in the steel melt by burst reaction.
  • According to the present invention, balls with the above functions are designed. The ball will decompose at a high temperature, and release micro bubbles as well as slag drops. By adding small particles of sodium carbonate into the steel melt, the micro bubbles will be generated in the steel melt. The micro bubbles are able to uniformize composition and temperature of the steel melt, and the inclusions are directly removed with capture and adsorption effects of the micro bubbles. According to the present invention, CaCO3, MgCO3, or (CaCO3 + MgCO3) composite powder is utilized as a situ agent for generating the micro bubbles. High-temperature decomposition of the CaCO3 and the MgCO3 are as follows:
    Figure imgb0001
    Figure imgb0002
  • According to researches, when carbonate powder is small enough, a size of a bubble generated is about a size of the powder. Therefore, the method is able to add ultra-fine bubbles into the steel melt (wherein the size of the bubble is between 100∼300µm). The smaller the bubbles are, the higher inclusion removal efficiency will be. In addition, alkaline earth oxides, another product of the decomposition reaction of carbonate, will be rapidly melted in the steel melt for forming the slag drops with a slag washing effect. Because of low reaction temperature of decomposition of the carbonates and poor thermal stability thereof, the disadvantage must be eliminated by reasonable designs. According to the present invention, the CaO, MgO, (CaO + MgO) composite powder or the white slags cool-collected by the ladle furnace is utilized as a carrier of the carbonate powder. By combining the carrier and the carbonate powder into the ball with a certain size, the thermal stability of the carbonate in the steel melt is improved.
  • Advantages of the present invention are as follows. Process is simple, and operation is convenient. Different balls are respectively added during the blast furnace tapping, the iron folding in the iron folding room, the converter tapping, and the late stage of the RH refining, so as to rapidly desulfurize, dephosphorize, and remove the small inclusions in the steel melt by slag-forming. Furthermore, the P and S contents in the steel are significantly reduced, while quantity and size distribution of small non-metallic inclusions remaining in the steel during refining is effectively controlled. With the method according to the present invention, S in the steel is controlled at 5∼20ppm, P is controlled at 20∼60ppm, the overall oxygen content is controlled at 3∼15ppm, and the inclusion equivalent diameter is controlled at 0.5∼10µm. Compared with the conventional process, raw materials utilized in the method are cheap, the cost for the steel per ton is reduced by 5-10 Yuan.
    • Detailed Description of the preferred Embodiment
  • These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting. It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.
    • Preferred embodiment 1
  • a method for preparing low-cost clean steel by which a cost is effectively lowered.
  • Accordingly, in order to accomplish the above object, the present invention provides a method for preparing low-cost clean steel, comprising steps of:
    1. 1) preliminarily desulfurizing iron melt: preliminarily desulfurizing in an iron melt channel during blast furnace tapping and during iron folding in an iron folding room, adding a desulfurizing ball into the iron melt during the blast furnace tapping or the iron folding, wherein an amount of the desulfurizing ball is 2∼8kg/t, in such a manner that S ≤ 0.01% by weight in the iron melt after preliminarily desulfurizing;
    2. 2) pre-desulfurizing the iron melt: finely desulfurizing the iron melt by dusting desulfurization with mixed powder of CaO and Mg powder, and filtering out desulfurized slags by a slag filter, in such a manner that after finely desulfurizing, S ≤ 0.0015% by weight in the iron melt before being sent into a converter;
    3. 3) dephosphorizing and controlling sulfur: dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P ≤ 0.014% and S ≤ 0.004% during tapping;
    4. 4) rapidly dephosphorizing by slag-forming: rapidly dephosphorizing by slag-forming during converter tapping; at a converter end point, controlling a C content at 0.02∼0.10%, controlling an oxygen activity value α o at 600∼1000ppm, adding a dephosphorizing ball through an alloy chute during the converter tapping, blowing argon and stirring at the same time, wherein an amount of the dephosphorizing ball is 3∼12kg/t, blowing strength of the argon is 30Nm3· 't-1·h∼150 Nm3·t-1·h, a blowing and stirring time of the argon is 0∼7min;
    5. 5) purifying steel melt during RH refining: adding a purifying ball at a late stage of the RH refining when a vacuum degree is at 66.7∼500Pa, wherein when adding the purifying ball, a downing tube is at an opposite side of a feeding opening; and
    6. 6) continuously casting with whole-process protection.
  • The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 20kg; CaO 50kg; CaF2 15kg; and CaCO3 15kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the desulfurizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 65kg; CaO 10kg; CaF2 1 kg; and CaCO3 5kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 10kg; CaO 65kg; CaF2 15kg; CaCO3 30kg; and Ca powder 15kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, and a particle size of the Ca powder is less than 1 mm.
  • MgO activity ≥ 200ml, and CaO activity ≥ 200ml.
    • Preferred embodiment 2
  • The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 55kg; CaO 20kg; CaF2 5kg; and CaCO3 5kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the desulfurizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 10kg; CaO 65kg; CaF2 15kg; and CaCO3 30kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 60kg; MgO 15kg; CaF2 1kg; MgCO3 5kg; and Mg powder 1 kg; particle sizes of the CaF2, MgCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, and a particle size of the Mg powder is less than 1 mm. Other features of the preferred embodiment 2 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
    • Preferred embodiment 3
  • The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 35kg; CaO 35kg; CaF2 10kg; and CaCO3 10kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the desulfurizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 38kg; CaO 38kg; CaF2 10kg; and CaCO3 12kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 35kg; mixed powder of CaO and MgO with any mixing ratio 40kg; CaF2 7kg; mixed powder of CaCO3 and MgCO3 with any mixing ratio 15kg; and Ca powder 1 kg; particle sizes of the CaO, CaF2, CaCO3, MgCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, and a particle size of the Ca powder is less than 1mm. Other features of the preferred embodiment 3 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
    • Preferred embodiment 4
  • The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45kg; CaO 40kg; CaF2 13kg; and CaCO3 12kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the desulfurizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 41kg; CaO 45kg; CaF2 5kg; and CaCO3 20kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 20kg; mixed powder of CaO and MgO with any mixing ratio 55kg; CaF2 3kg; CaCO3 20kg; and Ca powder 12kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, and a particle size of the Ca powder is less than 1mm. Other features of the preferred embodiment 4 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
    • Preferred embodiment 5
  • The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 25kg; CaO 30kg; CaF2 8kg; and CaCO3 14kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the desulfurizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 20kg; CaO 55kg; CaF2 12kg; and CaCO3 10kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 40kg; MgO 30kg; CaF2 11 kg; mixed powder of CaCO3 and MgCO3 with any mixing ratio 25kg; and mixed powder of Ca powder and Mg powder with any mixing ratio 13kg; particle sizes of the CaF2, CaCO3, MgCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, and particle sizes of the Ca powder and Mg powder are less than 1 mm. Other features of the preferred embodiment 5 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
    • Preferred embodiment 6
  • The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 30kg; CaO 45kg; CaF2 6kg; and CaCO3 9kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the desulfurizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 50kg; CaO 25kg; CaF2 8kg; and CaCO3 22kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 50kg; CaO 20kg; CaF2 4kg; MgCO3 10kg; and Ca powder 5kg; particle sizes of the CaO, CaF2, MgCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, and a particle size of the Ca powder is less than 1mm. Other features of the preferred embodiment 6 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
    • Preferred embodiment 7
  • The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 50kg; CaO 48kg; CaF2 7kg; and CaCO3 9kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the desulfurizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45kg; CaO 25kg; CaF2 3kg; and CaCO3 8kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45kg; CaO 25kg; CaF2 5kg; MgCO3 15kg; and Mg powder 4kg; particle sizes of the CaO, CaF2, MgCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, and a particle size of the Mg powder is less than 1mm. Other features of the preferred embodiment 7 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
    • Preferred embodiment 8
  • The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45kg; CaO 25kg; CaF2 12kg; and CaCO3 7kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the desulfurizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 28kg; CaO 35kg; CaF2 13kg; and CaCO3 18kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, the dephosphorizing ball is produced by dry-pressing, a size thereof is 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s;
  • The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 25kg; mixed powder of CaO and MgO with any mixing ratio 35kg; CaF2 13kg; CaCO3 7kg; and mixed powder of Ca powder and Mg powder with any mixing ratio 11 kg; particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm, and particle sizes of the Ca powder and Mg powder are less than 1 mm. Other features of the preferred embodiment 8 are the same as the features of the preferred embodiment 1, and will not be illustrated again.
    • Comparison
  • A conventional method for preparing clean steel comprises steps of:
    1. 1) pre-desulfurizing the iron melt: finely desulfurizing the iron melt by dusting desulfurization with mixed powder of CaO and Mg powder, and filtering out desulfurized slags by a slag filter, in such a manner that S ≤ 0.0020% by weight in the iron melt after finely desulfurizing;
    2. 2) dephosphorizing and controlling sulfur: dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P ≤ 0.014% and S ≤ 0.004% during tapping;
    3. 3) purifying steel melt during RH refining; and
    4. 4) continuously casting with whole-process protection.
  • By sampling at a 1/4 position of an inner arc of a casting bank, analyzing sharps and particle sizes of inclusions with a 500x microscope, analyzing an inclusion area content (within an area of 10×10mm) by quantitative metallography, and analyzing a total oxygen content by a nitrogen and oxygen analyzer, total oxygen, inclusion, P and S contents were detected by chemical analysis and are illustrated in Table 1.
  • According to the preferred embodiments and comparison in the Table 1, test data of S and P control, total oxygen control, and inclusion control in the steel illustrate that the method according to the present invention is superior to the method in the comparison in both single control and overall control. Furthermore, for the high-quality steel provided by the present invention, S in the steel is controlled at 5∼20ppm, P is controlled at 20∼60ppm, the overall oxygen content is controlled at 3∼15ppm, and the inclusion equivalent diameter is controlled at 0.5∼10µm. Table 1
    Embodiment Total oxygen Max inclusion Average inclusion area P (ppm) S (ppm)
    Preferred embodiment 1 14 8.34 0.00803 30 20
    Preferred embodiment 2 10 7.1 0.005 20 20
    Preferred embodiment 3 8 6.2 0.004 50 10
    Preferred embodiment 4 6 5.2 0.003 40 10
    Preferred embodiment 5 6 6.8 0.0035 50 6
    Preferred embodiment 6 4 4 0.0015 30 5
    Preferred embodiment 7 15 9.5 0.0091 50 20
    Preferred embodiment 8 10 8.8 0.0085 40 20
    Comparison 26 39.7 0.01239 100 50

Claims (9)

  1. A method for preparing low-cost clean steel, comprising steps of:
    1) preliminarily desulfurizing iron melt: preliminarily desulfurizing in an iron melt channel during blast furnace tapping and during iron folding in an iron folding room, adding a desulfurizing ball into the iron melt during the blast furnace tapping or the iron folding, in such a manner that after preliminarily desulfurizing, S ≤ 0.01% by weight in the iron melt before being sent into a converter;
    2) pre-desulfurizing the iron melt: finely desulfurizing the iron melt by dusting desulfurization, and filtering out desulfurized slags by a slag filter, in such a manner that S ≤ 0.0015% by weight in the iron melt after finely desulfurizing;
    3) dephosphorizing and controlling sulfur: dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P ≤ 0.014% and S ≤ 0.004% during tapping;
    4) rapidly dephosphorizing by slag-forming: rapidly dephosphorizing by slag-forming during converter tapping; an a converter end point, controlling a C content at 0.02∼0.10%, controlling an oxygen activity value α o at 600∼1000ppm, adding a dephosphorizing ball through an alloy chute during the converter tapping, blowing argon and stirring at the same time;
    5) purifying steel melt during RH refining: adding a purifying ball at a late stage of the RH refining when a vacuum degree is at 66.7∼500Pa; and
    6) continuously casting with whole-process protection;
    wherein the desulfurizing ball comprises: white slags cool-collected by a ladle furnace 20∼55%, CaO 20∼50%, CaF2 5∼15%, and CaCO3 5∼15% by weight, wherein particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm;
    wherein the dephosphorizing ball comprises: white slags cool-collected by a ladle furnace 10∼65%, CaO 10∼65%, CaF2 1∼15%, and CaCO3 5∼30% by weight, particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm; and
    wherein the purifying ball comprises: white slags cool-collected by a ladle furnace 10∼60%, CaO 15∼65%, CaF2 1∼15%, CaCO3 5∼30%, and Ca powder 1∼15% by weight, particle sizes of the CaO, CaF2, CaCO3 and the white slags cool-collected by the ladle furnace are less than 100µm.
  2. The method, as recited in claim 1, wherein in the step 1), an amount of the desulfurizing ball is 2∼8kg/t.
  3. The method, as recited in claim 1, wherein in the step 4), an amount of the dephosphorizing ball is 3∼12kg/t, blowing strength of the argon is 30Nm3·t-1·h∼150 Nm3·t-1·h, a blowing and stirring time of the argon is 0∼7min.
  4. The method, as recited in claim 1, wherein in the step 5), when adding the purifying ball, a downing tube is at an opposite side of a feeding opening.
  5. The method, as recited in claim 1, wherein the desulfurizing ball, the dephosphorizing ball and the purifying ball are all produced by dry-pressing, sizes thereof are 5∼25mm, compression strength thereof is 5∼35MPa, and a reaction time of delay burst at 1600°C is 1∼35s.
  6. The method, as recited in claim 1 or 4, wherein the CaO in the purifying ball comprises MgO and CaO with any mixing ratio.
  7. The method, as recited in claim 1 or 4, wherein the CaCO3 in the purifying ball comprises MgCO3 and CaCO3 with any mixing ratio, and a particle size of the MgCO3 is less than 100µm.
  8. The method, as recited in claim 1 or 4, wherein the Ca in the purifying ball comprises Mg powder and Ca powder with any mixing ratio, and particle sizes of the Mg powder and the Ca powder are less than 1 mm.
  9. The method, as recited in claim 1, wherein MgO activity ≥ 200ml, CaO activity ≥ 200ml.
EP12871396.3A 2012-03-13 2012-03-13 Process for producing low-cost clean steel Active EP2816125B1 (en)

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CN112779458A (en) * 2020-12-28 2021-05-11 日照钢铁控股集团有限公司 Method for controlling inclusions in pipeline steel
CN113512618A (en) * 2021-04-02 2021-10-19 首钢京唐钢铁联合有限责任公司 Refining duplex method for effectively controlling inclusions
CN113718081A (en) * 2021-08-04 2021-11-30 邯郸钢铁集团有限责任公司 Method for increasing number of continuous drawing furnaces of sulfur-containing gear steel

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CN114367657B (en) * 2021-12-08 2023-07-14 鞍钢股份有限公司 Torpedo ladle iron folding speed control method based on hot metal ladle weighing

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CN112779458A (en) * 2020-12-28 2021-05-11 日照钢铁控股集团有限公司 Method for controlling inclusions in pipeline steel
CN112779458B (en) * 2020-12-28 2022-03-11 日照钢铁控股集团有限公司 Method for controlling inclusions in pipeline steel
CN113512618A (en) * 2021-04-02 2021-10-19 首钢京唐钢铁联合有限责任公司 Refining duplex method for effectively controlling inclusions
CN113718081A (en) * 2021-08-04 2021-11-30 邯郸钢铁集团有限责任公司 Method for increasing number of continuous drawing furnaces of sulfur-containing gear steel

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KR20140121452A (en) 2014-10-15
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EP2816125A4 (en) 2015-03-04
WO2013134889A1 (en) 2013-09-19
US9708676B2 (en) 2017-07-18
US20150027656A1 (en) 2015-01-29
JP5876168B2 (en) 2016-03-02
EP2816125B1 (en) 2015-11-25

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